Method and device for d2d communication within a cellular radio network

ABSTRACT

A method of and device for generation and transmission of a first data message over a wireless channel and for a device-to-device enabled cellular communication device arranged to operate with a cellular radio access network. A transmitter identification, ID, of the cellular communication device in the first data message is included. The entire first data message, including at least data associated with the transmitter ID is scrambled with a scrambling sequence associated with a synchronisation source identity. The first data message is transmitted over the wireless channel. A corresponding method of and device for receiving and decoding one or more data messages over a wireless channel and for a device-to-device enabled cellular communication device arranged to operate with a cellular radio access network. A first synchronisation source identity is determined. A received first data message with a scrambling sequence associated with the first synchronisation source identity is descrambled. The received first data message is decoded. A transmission identity, ID, is determined from the first data message.

TECHNICAL FIELD

The present invention generally relates to a method of generation andtransmission of a first data message over a wireless channel and for adevice-to-device enabled cellular communication device arranged tooperate with a cellular radio access network, and a method of receivingand decoding one or more data messages over a wireless channel and for adevice-to-device enabled cellular communication device arranged tooperate with a cellular radio access network, and to such acommunication device, and a computer program for implementing themethods.

BACKGROUND

In a cellular deployment, scrambling sequences are controlled by theeNodeB such that both the User Equipment, UE, and the eNodeB always knowwhat scrambling sequence is applied by each UE and for each channel andresource. However, for device-to-device, D2D, communication, a centralnode performing scheduling and controlling all UEs in proximity islacking, e.g., for Out of network Coverage, OoC. Furthermore, UEs inproximity might be controlled by different eNodeBs or control nodes.Because of the above, UEs may be unaware of the scrambling sequencesused by neighbour UEs when transmitting their channels/signals.

In 3GPP LTE, the device only needs to de-scramble sequences form theserving cell. D2D broadcast communication introduce some new aspects ofthe lower layer scrambling, mainly how to handle—from a devicecomplexity point of view—the case of a device OoC and capable to receiveD2D broadcast communication, or a D2D discovery signal. A device OoC maynot have information of scrambling sequences used for the D2D broadcastcommunication and in order to reduce such device scrambling search spacean efficient scrambling procedure is needed. Furthermore in D2Dcommunication a device should also be able to receive broadcastcommunication from other devices in another cell than the receivingdevice. This put also requirements on the device to be able todescramble sequences for many different cells, and an exhaustive searchover all potential scrambling sequences is very complex.

Therefore there is a need for methods and apparatus for efficientscrambling identification while still fulfilling the requirements ofrandomized sequences and identification of sequences destined for aparticular device.

SUMMARY

Some embodiments intends to solve the problem of how toscramble/descramble sequences such that the device easily can, in a lowcomplexity way, identify the scrambled sequence used and hence decodethe message while still having randomized scrambling behaviour.

Some embodiments are based on the understanding that properscrambling/descrambling can be achieved by transmitting a first D2Dmessage from a first device with a first identity, the message includesat least an identity of the synchronization source used by the firsttransmitting device, and the message is scrambled with a scramblingsequence associated with a synchronization source used by thetransmitting device, whereby the receiving entity can identifyinformation from which it can associate the correct scrambling sequencefor descrambling.

According to a first aspect, there is provided a method of generationand transmission of a first data message over a wireless channel and fora device-to-device enabled cellular communication device arranged tooperate with a cellular radio access network. The method comprisesincluding a transmitter identification, ID, of the cellularcommunication device in the first data message; scrambling the entirefirst data message, including at least data associated with thetransmitter ID, with a scrambling sequence associated with asynchronisation source identity; and transmitting the first data messageover the wireless channel.

The synchronisation source may be a controlling node to which thecellular communication device is associated by the cellularcommunication device is camping on the controlling node, is served bythe camping node or controlled by the controlling node.

The synchronisation source may be the cellular communication device. Thefirst data message may be transmitted at predetermined frequency/timeresources.

The scrambling sequence associated with a synchronisation sourceidentity may be derived from a Primary Synchronisation Source Identity,PSSID

The method may further comprise scrambling a checksum associated withthe first data message, wherein the scrambling of the checksum may bemade with a scrambling sequence associated with and identity of areceiver of the first data message; and then performing the scramblingof the entire first message. The checksum may be a cyclic redundancycheck. The identity of the receiver may be either received from thefirst synchronisation source or preconfigured.

The method may further comprise scrambling a second data message with asequence associated with the transmitter ID of the cellularcommunication device; and transmitting the second data message over thewireless channel.

The method may further comprise, prior to any transmission of the datamessage or messages, transmitting a synchronisation sequence, whereinthe synchronisation sequence may be associated with an identity of thesynchronisation source.

The data message or messages may be transmitted at frequency/timeresources assigned by the synchronisation source.

The data message or messages may be a scheduling assignment message fordevice-to-device communication.

The cellular radio access network may be a 3GPP LTE cellular radioaccess network.

According to a second aspect, there is provided a method of receivingand decoding one or more data messages over a wireless channel and for adevice-to-device enabled cellular communication device arranged tooperate with a cellular radio access network. The method comprisesdetermining a first synchronisation source identity; descrambling areceived first data message with a scrambling sequence associated withthe first synchronisation source identity; decode the received firstdata message; and determining a transmission identity, ID, from thefirst data message.

The decoding of the first data message may comprise descrambling achecksum with a sequence associated with the receiver identity.

The method may further comprise descrambling a second data message witha scrambling code associated with the determined transmission ID.

The receiver identity may be determined from preconfigured capability ofthe cellular communication device.

The receiver identity may be received from a second synchronisationsource.

The first and second synchronisation sources may be idem.

The method may further comprise, prior to any reception of the datamessage or messages, receiving a synchronisation sequence, wherein thesynchronisation sequence may be associated with an identity of the firstsynchronisation source, wherein the determining of the firstsynchronisation source identity is based on the synchronisationsequence.

According to a third aspect, there is provided a communication devicefor operating with a cellular radio access network and enabled fordevice-to-device communication. The communication device comprises atransceiver arranged to transmit or receive one or more data messagesover a wireless channel; and a controller arranged to generate or decodeone or more data messages according to the first and/or the secondaspect.

According to a fourth aspect, there is provided a computer programcomprising instructions which, when executed on a processor of acommunication device, causes the communication device to perform themethod according to the first and/or second aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as additional objects, features and advantages of thepresent invention, will be better understood through the followingillustrative and non-limiting detailed description of preferredembodiments of the present invention, with reference to the appendeddrawings.

FIG. 1 shows some general D2D broadcast communication scenarios.

FIG. 2 is a flow chart illustrating a method according to an embodiment.

FIG. 3 is a flow chart illustrating methods according to embodiments forthe transmitter side.

FIG. 4 is a flow chart illustrating methods according to embodiments forthe receiver side.

FIG. 5 illustrates a potential contention problem that can be relievedby CRC.

FIG. 6 is a block diagram schematically illustrating a UE according toan embodiment.

FIG. 7 schematically illustrates a computer-readable medium and aprocessing device.

DETAILED DESCRIPTION

Some abbreviations

FDD Frequency Division Duplex

TDD Time Division Duplex

UL Uplink

DL Downlink

NW Network

RRC Radio Resource Controller

SIR Signal-to-Interference Ratio

SINR Signal-to-Interference-and-Noise-Ratio

SIM Subscriber Identification Module

TX Transmitter

RX Receiver

TRX Transceiver

UE User Equipment

RNTI Radio Network Temporary Identifier

CRC Cyclic Redundancy Check

PDCCH Physical Downlink Control Channel

PDSCH Physical Downlink Synchronisation Channel

ID Identifier

XOR eXclusive-OR

Other abbreviations are explained as they appear throughout the text.

Although the approach of enabling D2D communications as a means ofrelaying in cellular networks was proposed by some early works on ad hocnetworks, the concept of allowing local D2D communications to (re)usecellular spectrum resources simultaneously with on-going cellulartraffic is relatively new. Because the non-orthogonal resource sharingbetween the cellular and the D2D layers has the potential of the reusegain and proximity gain at the same time increasing the resourceutilization, D2D communications underlying cellular networks hasreceived considerable interest in the recent years.

Specifically, in 3GPP LTE networks, such LTE Direct (D2D) communicationcan be used in commercial applications, such as cellular networkoffloading, proximity based social networking, or in public safetysituations in which first responders need to communicate with each otherand with people in the disaster area which is addressed in thefeasibility study of 3GPP TR 22.803.

D2D communication entities using an LTE Direct link may reuse the samephysical resource blocks (PRB), i.e. frequency/time (f/t) resources, asused for cellular communications either in the downlink or in the uplinkor both. The reuse of radio resources in a controlled fashion can leadto the increase of spectral efficiency at the expense of some increaseof the intra-cell interference. Typically, D2D communicating entitiesuse UL resources such as UL PRBs or UL time slots, but conceptually itis possible that D2D, e.g. LTE Direct, communications takes place in thecellular DL spectrum or in DL time slots. For ease of presentation, inthe present disclosure we assume that D2D links use uplink resources,such as uplink PRBs in an FDD or uplink time slots in an a cellular TDDsystem, but the approaches would carry over to cases in which D2Dcommunications take place in DL spectrum as well.

D2D communication in LTE should work in several scenarios. FIG. 1 showssome general D2D broadcast communication scenarios which should be ableto operate in. FIG. 1 also shows a first embodiment of the inventionrelated to a transmitting device (may also be UE, modem, sensor, smartphone, M2M type, Laptop, etc.). Note that in all cases the communicationmay be on the same frequency carrier. Hence the out of network coveragecase may use a subset of the f/t resources the controlling node use forcellular (and NW assisted D2D) communication.

However, several problems may be envisioned by use of the resources, forinstance:

A. The communicating devices are inside coverage of a controlling node,acting as a synchronization source. The controlling node may be an eNodeB or a UE assuming the control role (Cluster Head). In this case thecontrolling node allocates the resources use for the communication.

B. All devices are outside NW coverage. In this case one of the devicesis a controlling node (i.e. Cluster Head) controlling the resourceallocation for the communication. The cluster head acts as asynchronization source

C. Some devices are in NW/CH coverage and some are outside. In thiscase, the NW/CH node is the controlling node and the synchronizationsource. An in-coverage UE may relay the controlling node synch signaland optionally synch and broadcast information from the controlling nodeto out-of-coverage UEs. In this case, the synchronization sourceidentifier and associated sequence is used also by the relay UE. Thesynchronization source identity may sometimes be referred to as physicallayer sidelink synchronization identity.

In addition to the broadcast communication application described above,additional applications may be implemented by D2D, both in coverage (IC)and out of coverage (OoC). In particular, this may apply for unicastcommunication where a certain transmission targets a specific receiver,and multicast communication where a specific data transmission targets aset of receivers.

Additionally, proximity detection may be achieved by D2D by periodicallytransmitting discovery beacons, i.e., messages carrying at least atransmitter identity. By successfully detecting such messages, areceiver may be aware of which other UEs that are in proximity.Proximity detection is often termed as discovery.

Lower layer scrambling of data channels in LTE is used for severalpurposes. First the physical channel (e.g. PDCCH/PDSCH) itself may bescrambled based on the transmitting eNodeB cell Identity. The main useof this scrambling is for randomization and interference reductionpurposes. The scrambling of the physical channels may be determined bythe receiving device based on cell ID information that is determined inthe cell search process, i.e. from the primary and secondarysynchronization channels (PSS/SSS).

Furthermore, in LTE there is also scrambling of the CRC of the PDCCH,that scrambling may be based on the RNTI. The PDCCH CRC scrambling isused in order to determine which PDCCH that is allocated for a specificdevice. The device receives the RNTI information from the serving orcamping cell, and hence has knowledge of which scrambling sequences toapply on the CRC for decoding the PDCCH allocated to the device.

An approach is to transmit a first D2D message from a first device witha first identity, the message includes at least an identity of thesynchronization source used by the first transmitting device, and themessage is scrambled with a scrambling sequence associated with asynchronization source used by the transmitting device. Thesynchronization source may be the serving cell, another UE (clusterhead) controlling the first device, or the first device itself.Furthermore prior to transmission of first message a synchronizationsignal sequence associated with the synchronization source may betransmitted. Furthermore a checksum of the first message may bescrambled by a sequences associated with a receiving device.Furthermore, a second message may be transmitted from the firsttransmitting device, the second message scrambled by a scramblingsequence associated with the transmitting device identity. A receivingdevice receiving and de-scrambling the D2D message(s) is disclosed. Thebasic principles of the approach are also disclosed in FIG. 2, which isa signal scheme. The signal scheme indicates a first data messageincluding TX ID, with optional CRC scrambled with a scrambling sequenceassociated with RX ID, scrambled with a sequence associated with asynchronisation source. The signal scheme also indicates an optionalsecond data message, also with an optional CRC scrambled with ascrambling sequence associated with RX ID, scrambled with a sequenceassociated with TX ID. The signal scheme also indicates asynchronisation sequence which is associated with an identity of thesynchronisation source.

FIG. 3 is a flow chart illustrating methods according to embodiments.Hashed boxes indicate optional steps. A data bit generation step 100generates data bits including TX ID. Thus, the transmitting devicegenerated data bits to be transmitted, and the data bits at leastincluding a synchronization source identity associated to thetransmitting device are generated. The synchronization source identitymay sometimes be referred to as physical layer sidelink synchronizationidentity. Optionally, CRC bits (checksum) are generated 110 based on thetransmitted data bits, and the CRC bits are scrambled, e.g. XORscrambling typically, but not limited to, with a bit sequence associatedwith the receiver identity RX ID. For example, 16 bits may be used forthe CRC. Typically, the scrambling is based on an RNTI value. The RNTImay be a broadcast RNTI, known to all devices capable to receive D2Dcommunication in LTE. It may also be a group RNTI known to a subset ofD2D capable devices. It may furthermore be a unicast RNTI, known only bya single D2D device. It may also be a transmitter identity associated tothe transmitting device. It may also be an RNTI associated to a resourceidentifier, related to a resource where a scheduling assignment wastransmitted, i.e. a scheduling assignment ID. The scheduling assignmentID may sometimes be referred to as sidelink scheduling assignmentidentity. Different types of RNTI, as described above, may be chosendepending if the data is intended to be broadcasted to any potentiallyinterested receiver, or if it is targeting a subset of receivers, i.e.multicast, or a single receiver, i.e. unicast. In case of broadcasttransmission, the RNTI should not be based on a specific receiveridentity. The device then generates 120 modulated symbols, e.g. BPSK,QPSK, 16-QAM, etc., and scramble, e.g. complex valued multiplication,the symbols with at least a sequence associated with at least thesynchronization source ID. The synchronization source identity maysometimes be referred to as physical layer sidelink synchronizationidentity. The scrambling sequence may be a QPSK sequence. Thesynchronization source may be an eNodeB, e.g. serving cell of thetransmitter device, or another UE, e.g., a Synchronization Cluster Headcontrolling/serving the transmitting device. The transmitting device mayfurthermore be a Cluster Head itself, and thereby the synchronizationsource. Optionally, prior to transmitting the first message,synchronization signals may be transmitted 130. The sync signal sequencemay be associated with the synchronization source identity, or to theidentity of the synchronization relayed by the synchronization source.Sync signals may be transmitted prior to the message, or on regularbasis, e.g. every 5-500 ms or so. Then the first data block or sequenceis transmitted 140 on configured time/frequency resources on a certaincarrier frequency. The time/frequency resources used is eitherpre-configured by standard or configured by the controlling node. Forexample, one synchronization subframe for D2D may be provided for eachperiodic instant. The synchronization subframe for D2D may comprise aprimary synchronization sequence, e.g. 2 symbols, a physical downlinksynchronization channel carrying information to support synchronizationmanagement, and a secondary synchronization sequence, e.g. 2 symbols.Optionally, the first data block or sequence comprises schedulingassignments 150 with information about a second data block or sequence.The information may include link adaptation details, modulation details,coding details, diversity and redundancy information, and/or a pointerto a second data block or sequence associated to the transmission.Optionally, a second data message is generated 160. This may be abroadcast, group-cast or a unicast message. Optionally, the data symbolsin the second message is scrambled 170 with a scrambling sequence, e.g.QPSK, associated with the transmitting device ID, or with a resourceidentifier related to the resource where the first data block orsequence was transmitted. Optionally, the second data message istransmitted 180.

FIG. 4 is a flow chart illustrating methods according to embodiments forthe receiver side. Optionally, the receiver receives a sync signalsequence 200 transmitted from the transmitting device. The receivingdevice may determine 210 a synchronization source ID. Thesynchronization source identity may sometimes be referred to as physicallayer sidelink synchronization identity. This may be determined from thesync signal sequence that is associated with a controlling node ID. Thedevice may determine the synchronization source ID in other ways aswell. For instance, the receiving device may have determined thesynchronization source ID from a cell search process, e.g. the physicalcell ID and sync source ID may be the same thing or linked to eachother, via for instance a one to one mapping. The device then receives220 a first data block or sequence transmitted from a transmittingdevice. The receiving device then, based on the determinedsynchronization source ID, descrambles 230 the received first data blockor sequence, with the scrambling sequence used that is associated withthe synchronization source ID. The mapping between synchronizationsource ID and the scrambling sequence may be pre-determined by standardand stored in the device. The first message is decoded 240. Optionally,the device de-scrambles 250 the CRC bits with a scrambling sequenceassociated with the receiver identity. Again the receiver identity,known to the receiving device, may be a broadcast, group-cast or unicastRNTI. The device determines 260 whether the data is to the receiver ornot. For instance, if the CRC is scrambled with a receiver identity, thedescrambled CRC indicates a match if the data is destined for thereceiving device. If the data is to the receiver, the receiving devicemay optionally receive 270 a second data sequence transmitted from thetransmitting device. Optionally, the receiver retrieves 280, in thefirst message, information such as second data sequence link adaptationdetails, modulation details, coding details, diversity and redundancyinformation, and/or a pointer at where to retrieve a second data blockor sequence associated to the transmission. Optionally, the secondsequence is descrambled 290 with a scrambling sequence associated withthe transmitting device ID.

FIG. 5 illustrates a potential contention problem that can be relievedby CRC. Two D2D devices are associated to the same synchronizationsource. This may mean that their transmitted data sequences arescrambled with the same synchronization source identity. Thesynchronization source identity may sometimes be referred to as physicallayer sidelink synchronization identity. In a non-limiting example,device A is transmitting a scheduling assignment, e.g. in the first datamessage, at one resource X, and device E is transmitting a schedulingassignment, e.g. first data message, at a different resource Y. If boththese scheduling assignments point at the same resource where bothdevice A and device E will transmit data, i.e. second data message,there will be contention. This contention can be resolved via CRC.

In one mode, the scheduling assignments include an RNTI (SA-RNTI) thatwill be used for scrambling the CRC for the second data message. Thisenables the receiver to resolve contention and only process the datawith a matching CRC from the scheduling assignment.

In a second mode, the scheduling assignments are associated to aresource index (SA-RNTI), describing the resource used for transmittingthe resource assignment, typically in relation to a known timereference. For example, assume that the available scheduling assignmentresources are associated with a 16-bit resource index, then the seconddata message is processed in consideration of the resource indexassociated to the resource where the scheduling assignment was sent.

On the receiver side, the receiver retrieves the SA-RNTI from the firstdata message, and uses the SA-RNTI for CRC with the decoded second databits.

FIG. 6 is a block diagram schematically illustrating a UE 300 accordingto an embodiment. The UE comprises an antenna arrangement 302, areceiver 304 connected to the antenna arrangement 302, a transmitter 306connected to the antenna arrangement 302, a processing element 308 whichmay comprise one or more circuits, one or more input interfaces 310 andone or more output interfaces 312. The interfaces 310, 312 can be userinterfaces and/or signal interfaces, e.g. electrical or optical. The UE300 is arranged to operate in a cellular communication network. Inparticular, by the processing element 308 being arranged to perform theembodiments demonstrated with reference to FIGS. 1 to 5, the UE 300 iscapable of communication within a 3GPP LTE network, and in particularLTE Direct, i.e. D2D, communication. The processing element 308 can alsofulfill a multitude of tasks, ranging from signal processing to enablereception and transmission since it is connected to the receiver 304 andtransmitter 306, executing applications, controlling the interfaces 310,312, etc.

The methods according to the present invention are suitable forimplementation with aid of processing means, such as computers and/orprocessors, especially for the case where the processing element 308demonstrated above comprises a processor handling D2D resource use asdiscussed above. Therefore, there is provided computer programs,comprising instructions arranged to cause the processing means,processor, or computer to perform the steps of any of the methodsaccording to any of the embodiments described with reference to FIG. 1to 5. The computer programs preferably comprises program code which isstored on a computer readable medium 400, as illustrated in FIG. 7,which can be loaded and executed by a processing means, processor, orcomputer 402 to cause it to perform the methods, respectively, accordingto embodiments of the present invention, preferably as any of theembodiments described with reference to FIGS. 1 to 5. The computer 402and computer program product 400 can be arranged to execute the programcode sequentially where actions of the any of the methods are performedstepwise. The processing means, processor, or computer 402 is preferablywhat normally is referred to as an embedded system. Thus, the depictedcomputer readable medium 400 and computer 402 in FIG. 7 should beconstrued to be for illustrative purposes only to provide understandingof the principle, and not to be construed as any direct illustration ofthe elements.

1. A method of generation and transmission of a first data message overa wireless channel and for a device-to-device enabled cellularcommunication device arranged to operate with a cellular radio accessnetwork, the method comprising: including a transmitter identification,ID, of the cellular communication device in the first data message;scrambling the entire first data message, including at least dataassociated with the transmitter ID, with a scrambling sequenceassociated with a synchronization source identity; and transmitting thefirst data message over the wireless channel.
 2. The method of claim 1,wherein the synchronization source is a controlling node to which thecellular communication device is associated by the cellularcommunication device is camping on the controlling node, is served bythe camping node or controlled by the controlling node.
 3. The method ofclaim 1, wherein the synchronization source is the cellularcommunication device.
 4. The method of claim 3, wherein the first datamessage is transmitted at predetermined frequency/time resources.
 5. Themethod of claim 1, wherein the scrambling sequence associated with asynchronization source identity is derived from a PrimarySynchronization Source Identity, PSSID.
 6. The method of claim 1,further comprising scrambling a checksum associated with the first datamessage, wherein the scrambling of the checksum is made with ascrambling sequence associated with an identity of a receiver of thefirst data message; and then performing the scrambling of the entirefirst message.
 7. The method of claim 6, wherein the checksum is acyclic redundancy check.
 8. The method of claim 6, wherein the identityof the receiver is one of received from the first synchronization sourceand preconfigured.
 9. The method of claim 1, further comprising:scrambling a second data message with a sequence associated with thetransmitter ID of the cellular communication device; and transmittingthe second data message over the wireless channel.
 10. The method ofclaim 1, further comprising, prior to any transmission of the first datamessage transmitting a synchronization sequence, wherein thesynchronization sequence is associated with an identity of thesynchronization source.
 11. The method of claim 1, wherein the firstdata message is transmitted at frequency/time resources assigned by thesynchronization source.
 12. The method of claim 1, wherein the firstdata message is a scheduling assignment message for device-to-devicecommunication.
 13. The method of claim 1, wherein the cellular radioaccess network is a 3GPP LTE cellular radio access network.
 14. A methodof receiving and decoding at least one data message over a wirelesschannel and for a device-to-device enabled cellular communication devicearranged to operate with a cellular radio access network, the methodcomprising: determining a first synchronization source identity;descrambling a received first data message with a scrambling sequenceassociated with the first synchronization source identity. decoding thereceived first data message; and determining a transmission identity,ID, from the first data message.
 15. The method of claim 14, where thedecoding of the first data message comprises descrambling a checksumwith a sequence associated with the receiver identity.
 16. The method ofclaim 14, further comprising descrambling a second data message with ascrambling code associated with the determined transmission ID.
 17. Themethod of claim 14, wherein the receiver identity is determined frompreconfigured capability of the cellular communication device.
 18. Themethod of claim 14, wherein the receiver identity is received from asecond synchronization source.
 19. The method of claim 18, wherein thefirst and second synchronization sources are idem.
 20. The method ofclaim 14, further comprising, prior to any reception of the data messageor messages, receiving a synchronization sequence, wherein thesynchronization sequence is associated with an identity of the firstsynchronization source, and wherein the determining of the firstsynchronization source identity is based on the synchronizationsequence.
 21. A communication device for operating with a cellular radioaccess network and enabled for device-to-device communication, thecommunication device comprising: a transceiver configured to one oftransmit and receive at least one data message over a wireless channel;and a controller configured to one of generate and decode at least onedata message by: for encoding: including a transmitter identification,ID, of the cellular communication device in the at least one datamessage; scrambling the entire at least one data message, including atleast data associated with the transmitter ID, with a scramblingsequence associated with a synchronization source identify; andtransmitting the at least one data message over the wireless channel;and for decoding: determining a first synchronization source identity;descrambling a received first data message with the scrambling sequenceassociated with the first synchronization source identity; decoding thereceived at least one data message; and determining the transmitter IDfrom the at least one data message.
 22. A computer storage mediumstoring a computer program comprising instructions which, when executedby a processor of a communication device for operating with a cellularradio access network and enabled for device-to-device communication,causes the communication device to perform a method comprising: forencoding: including a transmitter identification, ID, of the cellularcommunication device in the at least one data message; scrambling theentire at least one data message, including at least data associatedwith the transmitter ID, with a scrambling sequence associated with asynchronization source identity; and transmitting the at least one datamessage over the wireless channel; and for decoding: determining a firstsynchronization source identity; descrambling a received first datamessage with the scrambling sequence associated with the firstsynchronization source identity; decoding the received at least one datamessage; and determining the transmitter ID from the at least one datamessage.